Sandpaper

ABSTRACT

AN IMPROVED FLEXIBLE ABRASIVE SHEET AND A PROCESS FOR PRODUCING THE SAME IS DISCLOSED. THE FLEXIBLE ABRASIVE SHEET INCLUDES A BACKING OF A COPOLYMER OF ETHYLENE AND ACRYLIC ACID HAVING A MELT INDEX AS DETERMINED BY ASTM TEST NO. D1238-57T OF FROM ABOUT 10 UP TO ABOUT 50 AND CONTAINS FROM ABOUT 15 UP TO ABOUT 20 PERCENT POLYMERIZED ACRYLIC ACID BASED ON THE WEIGHT OF THE COPOLYMER, AND AN ABRASIVE GRIT PARTIALLY EMBEDDED IN THE ETHYLENE-ACRYLIC ACID COPOLYMER BACKING. THE FLEXIBLE ABRASIVE SHEET IS FREE OF ANY ADHESIVE OR BONDING AGENT BETWEEN THE BACKING AND THE ABRASIVE GRIT.

May 28, 1974 R. E. GILBERT ETAL SANDPAPER Filed July 3l, 1972 -clcrylEhylene ic Acid Copolymer ive m Abres Unted States Patent O 3,813,231SANDPAPER Ronald Edward Gilbert, Orange, Tex., aud Richard Leo Monley,Jr., Kansas City, Kans., assignors to Gulf Research & DevelopmentCompany, Pittsburgh, Pa. Filed July 31, 1972, Ser. No. 276,574 Int. Cl.B24b 37/00 U.S. Cl. 51--298 4 Claims ABSTRACT OF THE DISCLOSURE Animproved exible abrasive sheet and a process for producing the same isdisclosed. The -flexible abrasive sheet includes a backing of acopolymer of ethylene and acrylic acid having a melt index as determinedby ASTM Test No. D1238-57T of from about 10 up to about 50 and containsfrom about 15 up to about 20 percent polymerized acrylic acid based onthe weight of the copolymer, and an abrasive grit partially embedded inthe ethylene-acrylic acid copolymer backing. The exible abrasive sheetis free of any adhesive or bonding agent between the backing and theabrasive grit.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to a flexible abrasive sheet or an improved substitute forconventional sandpaper. In a more particular aspect, the inventionpertains to a backing for an abrasive which is similar to but has anumber of advantages over conventional sandpaper. The present inventionrelates not only to the abrasive backing but also to the completeabrasive paper, board, belt, Wheel, or the like. The instant inventionis concerned not only with the abrasive material and the paper orbacking for the abrasives but also to a method of producing the abrasivesheet, sandpaper, or the like. These coated abrasive products may bemade in the form of sheets, discs, belts, or the like and are known inthe art as int papers, garnet papers, emery cloth, sanding belts,abrasive discs, etc.

Description of the prior art In many instances in the prior art, thelife service of abrasive belts, papers, discs and other abrasive bodiesincluding the particles or other abrasive materials employed in theseabrasive bodies has been comparatively limited. Numerous causes havecontributed to early failure and poor functioning of many of the priorart abrasive bodies. One of the contributing factors is the strength ofthe backing material which has often been limited and the flexibility ofthe same which in many cases has been poor. Another factor has been thatthe individual abrasive particles of the abrasive material have not beensufficiently bonded or held to the abrasive backing such that theparticles have often quickly become dislodged from the backing and theabrasive material has been depleted of abrasive particles on itssurface. In the past, the customary method of producing an abrasivesurface has usually consisted of bonding abrasive particles or grit to abacking using adhesives such as glues, resins or plastics.

Coated abrasive products have in recent years become industriallyimportant due in part to their enhanced cutting abilities whencontrasted with solid bonded adhesive products, and also because of thegreater convenience in adopting coated abrasive products to intricatecontour grinding. In the present state of the coated abrasive art,reliance is had mainly on relatively rigid binders or adhesives forbonding the abrasive grains or particles to the backing of the product,since retention of the surface abrasive grains is of primary importancefor economy of service. Accordingly, most of the conventional abrasivecoated products utilize as the bonding adhesive natural or syntheticglues, phenolaldehyde resins or modifications thereof.

In spite of the substantial industrial acceptance of coated abrasiveproducts, their use has been limited or restricted for a number ofreasons. Due to the hard or rigid character of many of the bondingadhesives used, the abrasive products are relatively rigid and stiff. Inthe abrading of surfaces of intricate convolutions and compound curves,it is diicult to properly abrade or polish such surfaces because of thenonconformability or stiffness of these conventionally made coatedproducts. Bending to achieve conformability to the object being abradedusually cracks the abrasive surface and at times the backing materialalso, Which can result in the loss of substantial amounts of abrasiveparticles or grits. For service Where greater resistance to such failures required, the backing material may be sized cloth such as cottontwill, chambric, etc. However, even with reliance on fabrics, theconventional adhesives are sufficiently rigid so that the end productretains suicient rigidity to promote cracking, spalling and breakagewhen used under extreme conditions of ex and deflection. The adhesivebond is faulty in its inability to distend, deform and stretchconsistent with the requisite adhesion of the abrasive grains to thebacking of the abrasive product. In use, the abrasive surface becomesprematurely loaded with abraded particles, which later stay embeddedbetween the grains of the abrasive surface impeding or inhibitingfurther abrading use of the abrasive product. The rigid adhesives arefurthermore relatively weak as a bond, resulting in the tendency of theabrasive grains to loosen and fall away particularly if worked oversurfaces other than flat.

SUMMARY OF 'I'HE INVENTION It is the general object of this invention toprovide an improved substitute for conventional sandpaper in the form ofa flexible abrasive product which may be produced without the use of anadhesive or bonding agent between the backing and the abrasive particlesor grit.

Another object of the subject invention is to provide a sandpapersubstitute of improved quality in the form of a -iiexible abrasive sheetwherein the loss of abrasive particles from the sheet when the same isemployed in abrading work is substantially reduced.

A further object of the invention is to provide an improved flexibleabrasive product which when compared with sandpaper and other Well knownconventional abrasive products has an increased life, has a backingwhich is extremely tough, is water resistant, has a long wearing lifeand is of a tacky nature such that the backside of same is easilygripped and will not slip in ones hand or other equipment with which theabrasive product is employed.

In general, these objects are attained by providing an improved abrasiveproduct and a process for producing the same, which product consistsessentially of a backing of a copolymer of ethylene and acrylic acid andan abrasive grit which is partially embedded in the ethyleneacrylic acidcopolymer backing. The abrasive product is free of and is producedwithout the use of any adhesive or bonding agent between the backing andthe abrasive grit.

BRIEF IDESCRIPTION OF THE DRAWING The novel features which are believedto be characteristic of this invention are set forth with particularityin the appended claims. The invention itself, however, both as to itsorganization and method of operation together with further objects andadvantages thereof may best be understood by reference to the followingdescription taken in connection with the accompanying drawing in which:

FIG. 1 is a perspective view of the improved abrasive product orsandpaper substitute of this invention;

FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT It has been found that animproved abrasive product or an improved substitute for conventionalsandpaper can be formed and produced without the use of an adhesive,bonding agent or binder between the abrasive particles or grit and thebacking, if the abrasive particles or grit (such as the sand used in themanufacture of conventional sandpaper) is partially pressed at anelevated temperature into the softened surface of a backing whichconsists of a film prepared from an ethylene-acrylic acid copolymer. Thesandpaper substitute or improved abrasive sheet prepared in accordancewith this invention is superior to conventionally prepared sandpapers inthat no adhesive or bonding agent is required between the abrasiveparticles and the backing. Furthermore, due to the tenacious grippingproperties and characteristics of the ethylene-acrylic acid copolymerfilm backing of the abrasive sheet, the individual granules or particlesof grit are not readily or easily pulled out or separated from the filmbacking. Additionally, the substitute sandpaper backing consisting of afilm prepared from an ethylene-acrylic acid copolymer, as designated bythe invention, has a markedly increased life when compared to thebacking of conventional sandpapers, such that the same will not readilywear through as with the backing of conventional sandpapers. Another bigadvantage of the abrasive sheet of this invention when compared toconventional sandpapers having paper or cloth backings is that theproduct of this invention is nonreactive with water. The improvedabrasive product of this invention also has the additional advantage anddesirable characteristic over conventionally prepared sandpaper ofpossessing a tacky backside or surface whereby the same is readilygripped without slipping or sliding by ones hand or the surface of otherequipment with which the abrasive product is employed, such as anelectric sanding machine.

The improved flexible abrasive product of this invention may be preparedin any desired form, depending upon the end use in which the abrasiveproduct is to be employed. This is to say that the abrasive product maybe fabricated in the form of a flexible sheet, a belt, a disc, a boardsuch as an emery board, or the same may be fabricated with a proper formor support into a wheel similar to an emery wheel or grinding disc. Thethickness of the film backing of the ethylene-acrylic acid copolymer isdetermined by and depends upon the end use to which the abrasive products to be put or employed. Typically and preferably, the thickness of thethermoplastic film backing of the abrasive product will range from about5 up to about 50 mils depending upon desired end use. The abrasiveparticles themselves or the grit may be any suitably hard substancewhich has been powdered for use as an abrasive. Suitable examples wouldinclude alumina, silicon carbide, emery, garnet, or other like grit, orrouge or the like for polishing.

The ethylene-acrylic acid copolymer from which the film backing of theimproved abrasive sheet or other like product of this invention isprepared should contain from about 5 up to about 3() percent acrylicacid based upon the weight of the copolymer. Preferably, the copolymerfrom which the film of the backing is prepared will contain in the rangeof approximately l5 up to approximately 20 weight percent polymerizedacrylic acid with the remainder thereof being polymerized ethylene. Themelt index of the ethylene-acrylic acid copolymer from which the filmbacking of the abrasive product is formed may be in the range of fromapproximately 0.5 up to about as determined by ASTM Test No. Dl238-57T.The ethylene-acrylic acid copolymer used will preferably have a meltindex of from about 10 up to about 50 as determined by theabove-identified test.

One method or process by which the improved abrasive product of thisinvention may be formed is initiated by forming the backing film from anethylene-acrylic acid copolymer. Pellets of the copolymer are formedinto a lm which is to be used as the backing of the abrasive product bypressing the same between the platens of a platen press at a sufiicienttemperature and pressure to convert the pellets to a homogeneous film.After the film had cooled, a uniform layer of an abrasive or grit wasevenly distributed over the surface of the same. Next, the combinationof film and abrasive particles were pressed in the platen press with theplatens thereof barely touching for a period of 30 minutes at atemperature in the range of from about 75 to about 100 C. After the 30minutes had elapsed, the film was removed from the press and it wasfound that the abrasive particles or grit were well bonded to the film.

With detailed reference to the drawing, the improved flexible abrasivesheet or sandpaper substitute of this invention 10 is seen to include asheet-like backing 12 which is a thermoplastic film prepared from acopolymer of ethylene and acrylic acid. `In a specific embodiment of theinvention, film backing 12 had a thickness of approximately 10 mils. Aspreviously set forth hereinabove, the ethylene-acrylic acid copolymermay possess a melt index in the range of 0.5 to 80, and preferably willhave a melt index of from about 10 up to about 50; all melt indexesbeing determined by ASTM Test No. D1238-57T. In one specific embodimentof the invention, the ethyleneacrylic acid copolymer employed in formingthe film backing 12 of the flexible abrasive sheet 10 possessed a meltindex of 40. Additionally, as described hereinbefore, the copolymer ofethylene and acrylic acid will have an acrylic acid content in the rangeof approximately 5 to 30 percent based on the weight of the copolymer,and preferably will contain from about 15 up to about 20 weight percentacrylic acid. In one specific embodiment of the invention, theethylene-acrylic acid copolymer employed in preparing the film backing12 of the flexible abrasive sheet 10 had an acrylic acid content of 18.1weight percent. The other portion or part of flexible abrasive sheet 10,which completes the same, is the abrasive or grit 14 which as has beenstated herein may be any suitably hard substance powdered for abrasiveuse such as alumina, silicon carbide, emery, garnet, or other like grit,or rouge or other like materials used in polishing. In one specificembodiment of the invention, the abrasive particles or grit employed wasa silicon carbide grit of a No. mesh. With particular reference to FIG.2, it can be readily observed that the film backing 12 and the abrasiveparticles or grit 14 make up and comprise the flexible abrasive sheet10, and that no adhesive or bonding agent is required or used betweenbacking 12 and abrasive or grit 14. In the figure, it can be seen thatthe abrasive particles 14 are partially embedded in and held by thesurface 16 of the film backing 12.

In order to illustrate the process of producing the improved flexibleabrasive sheet of this invention, the

abrasive sheet itself, and some of its improved properties with greaterparticularity, the following specific examples are included, not onlyfor illustrative purposes -but also for comparative purposes. Theexamples are intended to illustrate only and are not intended to limitthe invention in any way.

EXAMPLE 1 This example illustrates the preparation of an improvedflexible abrasive sheet or sandpaper substitute of the invention. Theproduct of this example will be used hereinafter as a basis forcomparison with other similarly formed abrasive sheets wherein thebackings thereof are prepared from other thermoplastic materials.

Pellets of an ethylene-acrylic acid copolymer were placed between theplatens of a platen press for pressing into a film. The copolymercontained approximately 18.1 weight percent acrylic acid and had a meltindex of about 40. A film of approximately mils in thickness was pressedon the platen press using a temperature of 225 F., a pressure of 150p.s.i. and a spacing between the platens of about 10 mils. After thepressed film had cooled, a layer of approximately i6 inch in thicknessof silicon carbide (Carborundum) grit of a No. 180 mesh size was evenlyand uniformly distributed on the surface of the pressed lm. Thiscombination was then placed in the platen press with the platens thereofbarely touching the respective sides of the combination at a temperatureof about 200 F. for a period of 30 minutes. After the 30 minute timeinterval had elapsed, the film was removed from the platen press and itwas observed that the Carborundum grit was Well bonded to the film. Thefilm was then trimmed to produce a sheet of lflexible abrasive materialsimilar to that depicted at reference numeral 10 in the figures of thedrawing. The flexible abrasive sheet produced in this example iscompared hereinbelow in Table I with other similar sheets produced inthe following examples.

EXAMPLE 2 A flexible abrasive sheet similar to that prepared in Example1 was fabricated in this example by the method and process set forth inExample l employing pellets of a high-pressure, low-density ethylenehomopolymer to form the film backing of the abrasive sheet. Thelowdensity, high-pressure polyethylene used had a melt index ofapproximately 2. The thus fabricated abrasive sheet in compared withother similarly prepared abrasive sheets hereinbelow in Table I.

EXAMPLE 3 In this example, a exible abrasive sheet similar to the onefabricated in Example 1 was prepared by the same procedure as that usedin Example 1 with the exception that pellets of a linear or high-densitypolyethylene were used in forming the film backing of the abrasivesheet. The linear polyethylene employed was a high-density, low-pressurepolyethylene marketed -by Phillips Petroleum Company under the tradedesignation Marlex 6003, and had a melt index of approximately 0.3. Theresultant flexible abrasive sheet is compared with other similarlyfabricated sheets in Table I hereinafter.

EXAMPLE 4 A flexible abrasive sheet similar to that obtained in Example1 was prepared in this example by the method and process of Example 1using pellets of a propylene homopolymer to form the film backing of thesheet in the platen press. The propylene homopolymer used had a meltindex of approximately 3. The exible abrasive sheet produced herein iscompared in Table I hereinbelow with other similarly prepared abrasivesheets.

'6 EXAMPLE 5 In this example, a -exible abrasive sheet similar to thatobtained in Example 1 was produced by the procedures of Example lemploying pellets of a copolymer of ethylene and methyl acrylate in theplaten press to form the thermoplastic film backing. The ethylene c0-polymer used in this example contained approximately 20 weight percentmethyl acrylate and had a melt index of approximately 2. The resultantabrasive sheet is compared wit-h other similarly fabricated abrasivesheets in Table I which follows.

Portions or` samples of each of the abrasive sheets prepared in theabove Examples 1 through 5, inclusive, were cut to t on the wheel of aTaber Abraser. This piece of laboratory equipment is used to give aquantitative analysis of the resistance to abrasion of various materialsused therewith. Each of the cut samples obtained from the exibleabrasive sheets prepared in the above examples was in turn placed on theTaber Abraser apparatus to run thereon under a (JS-17 Calibrase wheelwhich was used with a 500 gram weight or load. This combination of loadand wheel produced a harsh abrasive effect. The results of each of thetests is set forth hereinbelow in Table I with the results beingexpressed in terms of a wear index.

TAB LE I Sample o Wt.,before Wt. after No. Wear Example abrasionabrasion Net loss cycles index 1o. 3289 10. 6593 0. 1696 1, 125 15o. s

lThe sample of Example 5 began to curl, bunch and roll up alter 7 cyclesunder the abrading wheel and, therefore, could not be run for the full1,125 cycles, evaluated and compared.

i' Very high.

As can be readily observed from the above table, the results of wearindex obtained using the sample of Example 1 is substantially lower thanthe result or wear index obtained with the samples of the otherexamples. The wear index determined for the Example l sample indicatesthat this particular sample possesses the greatest resistance toabrasion of the various sheets or abrasion products tested and comparedin the table. The low wear index determined for the sample of Example 1,the abrasive sheet having a film backing prepared from anethylene-acrylic acid copolymer, indicates that the abrasive particlesor gritlof the sheet are more securely held in the backing than with thesheets of the other examples, and that the loss of abrasive particlesfrom the sheet during abrasive work-is substantially reduced and lessthan that of the sheets of the other examples.

While only certain preferred embodiments of the invention havebeendescribed and illustrated, many modifications and variations willoccur to those skilled in the art. It is, therefore, to be understoodthat, within the scope of the appended claims, the invention may bepracticed otherwise than as specifically described. y

What is claimed as new and what it is desired to secure by LettersPatent of the United States is:

1. An improved abrasive product consisting essentially of a backing of acopolymer of ethylene and acrylic acid and an abrasive grit partiallyembedded in said ethyleneacrylic acid copolymer backing, said abrasiveproduct being free of any adhesive or bonding agent between said backingand said abrasive grit.

2. The improved abrasive product as set forth in claim 1 wherein saidethylene-acrylic acid copolymer contains from about 5 up to about 30percent polymerized acrylic acid based on the weight of said copolymerand, correspondingly, about to about 70 weight percent polymerizedethylene.

3. The improved abrasive product as set forth in claim 2 wherein saidethylene-acrylic acid copolymer contains from about 15 up to about 20percent polymerized acrylic acid based on the weight of said copolymer.

4. The improved abrasive product as set forth in claim 3 wherein saidethy1eneacrylic acid copolymer contains about 18.1 weight percentpolymerized acrylic acid and said abrasive grit is silicon carbide.

8 References Cited UNITED STATES PATENTS 2,899,288 8/ 1959 Barclay51-298 3,637,428 1/ 1972 Aleckner 117-138.8

DONALD I. ARNOLD, Primary Examiner U.S. Cl. X.R. 51-295

